Electrical distribution system



Oct. 3, 1961 w. c. wlLKlNsoN 3,003,034

ELECTRICAL DISTRIBUTION SYSTEM Filed July 16, 1958 4 Sheets-Sheet -1 INVENTOR ,VC-mv C. /MM50 W 7 M ATTORNEY Oct. 3, 1961 w. c. WILKINSON ELECTRICAL DISTRIBUTION sYsTzu 4 Sheets-Sheet 2 Filed July 16, 1958 INVENTOR II f i waavv c. MMM/5M,

A FTORNEY Oct. 3, 1961 w. c. wlLKlNsoN ELECTRICAL nrsmsu'rron sysma 4 Sheets-Sheet 3 Filed July 16, 1958 Oct. 3, 1961 w. c. WILKINSON ELECTRICAL DISTRIBUTION sys'rm 4 Sheets-Sheet 4 Filed July 16, 1958 INVENTOR.

- i A 30035084, v ELECTRICAL DISTRIBUTION SYSTEM Weldon C, Wilkinson-, Bal`tiinore,Md., assignor to Rowan Contrgeir'company, Baltimore, Md., a corporation of Mary t Filed July 1,6', 195s, ser. No; 149,580

' 5 claims. (ci. 311-99) f This invention relates to an electrical distribution system, rand more particularly,` the invention relates to an electrical distribution system for factories and the like requiring a nmber of outletsfor supplying current to a large number of motor installations Aand the like.

Inaccordance 'with Ithe present `practice, plants having need `for operatingla number of heavy motors substantially independently, willl locate such motors a-t thei-r.

proper positions and'run heavy cable rto a central power supply; Associated 4with the central power supply are known control devices for selectively'operating the motors as desired. Such installations havefthe princi-paldisadvantage `thatfor each motor or the like 4the heavy cablewhich carries thecurrent to the motor must be installed from the control center to the motor in accordance with the existing yelectrical codes. Not only does the original installation require va complex system of cables all over the plant, but to rearrange machinery for changingthe original installation to a dilerent type of operation, requires the destruction of the existing system and relins'tallationl of acompletely new system. It is the object of vthe present invention vvto' `eliminate the `disadvantages of the presentpracticeewith its central control andl supply system. The 'principal disadvantages are eliminated and the object attained by providing a mainbusmountedjall aroun'dthe'- walls of the plant anden'closedy in'ak bus duct. Spaced along -the bus duct (approximately lft inehes on center, fory example) Kare outletspreferably consisting of line Vterminal blocks, termina-l `blocksare permanently mounted on thefbusduct]and,'when'not.inuse, areencased or covered so astolleaveno exposed'live contacts. Each of the terminal'"blocks, however, is permanently electrically connectedto the busor cable so that by pulling oi the cover of the terminal block or outlet, the hot contacts are exposed.

It is to be understood that when the term .bus is used, reference is made Ito non-insulated conductors or insulated cable. j

The principal advantage of the:arrangement according to the invention is that outlets yfor all electricalinstalla tions" are readilyavailable` afterv the original installation ofthe bus ductand outletfsy'sterml Thus, eithery the installation of new equipment or" thev subsequent .rearrangement of existing equipmentalsoy can be easily accomplished. v v

Further, thesystemin accordance with the-present invention permits Ya pressurizing ofthe current carrying and switching components in hazardous areas. Inaccordance 'with present practice, such'hazardous areas-are maintained rcompletely under'ipiessurelso that the' whole room is being continuously exhausted .in order to' avoidy the ignition of orillllSl-ilflle'`gt1tsesvby artisl dwilfby the switching components. In'aecor'dance with'theflpresent invention, the bus duct and switching assembly `is connected tofa `supply offgs "unde'rg pressure ,soj thatithe pressure"inthe:system is gieateiiftlarifatmospheric` Thus, if is impassible for` airy ebibiisitbief gases te get me the' lswiwhrng 'meehaiisn where a are is' `natie lel Caine anlexplosion.

Another object"7 of theini'enti""is"to* mount' the switching 'mechanism` whi'chfwdul consist' of adiscon necting switch or circuiti" breaker `a`mag'net icallyl operated" contacter, and possibly??` an over'erret relay, or

ICC

'2 v any combination of such units, on theV bus duct with an interlock arrangement bywhich the switching mechanism could not Abe dismounted without disconnecting the main switch or circuit breaker. This is not only a valuable safety feature from the standpoint of the electrical hazard, but it insures-that -there will be no arcing such as might ignite combustible gases when the assembly is being dismounted.

Another object of the invention is to provide a bus duct and outlet system as described'with a housing for electrical components extending ldownfrom they duct,

` and a cable tray mounted behind the housing' and spaced below the duct.

In' an alternative form of the invention, instead of hanging combination starters from a horizontally disposed bus duct, vertical bus drops connected to the main horizontalv bus areencased in vertical ducts and are spaced along'ithe horizontal duct. Adjoining each vertical duct but physically isolated therefrom is a 'cable duct through which are passed the cables to the motors orthe like energized' byV the system. The combination starterhousings aremounted adjacent `the vert-ical bus duct and the vertical cable 'duct and are physically isolated from each. A pluralityof such housings may be horizontallyV disposed and spacedwexticallyalong ythe vertical ducts. s f

The alternative arrangement Anot onlyr provides the isolation feature which serves -to localize damage by lire; but also provides economy of space `andi convenience of use antfinstallation.- of thel damage the invention avoids is -theashioccurring upon failure of a unit. In theV absence of Ythe invention, Athis ilash would carbonize the Asurrounding electrical equipmentand ycause aco'stly shutdov'vn.' ,'Still furtherfthe isolation ofthe various nnits,'cable :and busducts localizes heati'dissipation thereby avoiding the chimney effect ofprior constructions; The' chimney etect resulted fromthe units dissipatin-g heat into -aaoommonductfwhich duct would .concentrate heat at the area of" the bus andcreate a high ambient temperature atthat location. The high ambient temperature in turn requires `the use of bus having ahigher rating-thanwould 4be yrequired if ambient were room temperature.

Itjis another objectof the'invention to provider a grommet for connecting adiacent compartments, such as control uni-t housing and cable duct,` in whichthe grom'niet has aiweb formed of separate sectors which snugly` embrace cable'passing-therethrough, thus completing the isolationf of adjacent compartments.`

It is stillfanother object of `the invention 'to provide a U-shaped bridge joini-ngvadjacent transverse"llangesl of cableY duct sections to'potect the cableinsulationv against w'eari-ng'ony the ange edges. v

These.` and'other objectsfof the invention willbecoine more readily.` apparent from Ithe following cdetailed `de scriptionbf 'the invention taken f in conjunction f with' the accompanying drawings in` which:Y

F1o; 1 isfapispeetive diagramme View snsw'ingav FIG. 8 is a side elevational view, partly in section of the alternative form;

FIG. 9 is an exploded view of the -top of the invention;

FIG. 10 is a fragmentary view of a connection between adjacent `duct sections;

FIG. 1l is a cross sectional view taken along lines 11-11 of FIG. 10:

FIG. l2 is a plan view of a grommet, and

FIG. 13 is a cross sectional view taken along lines 13-13 of FIG. 12.

Referring to FIG. l, three walls of a room of a plant are indicated at 10. Mounted by means of brackets 12 is an elongated bus duct 14 extending around the periphery of the plant. It is to be understood that the bus duct could cross the plant intermediate the walls or could be mounted to the ceiling as shown at 11 if advisable.

ther arrangements such as self contained, insulated stations 13 comprising racks supporting ducts with varying numbers of outlets could be used depending on the particular plant arrangement. Further, it is within the scope of the invention to make installations outside the plant building as shown at 15.

Inside the bus duct ,are Ibuses or cables 16 which are mounted in suitable supports 18 (FIG. 2)V of insulating material in a known manner. Substantially uniformly spaced around the room on the bus duct are outlets 20, to be described in detail below.

An assembly of housings 22 for electrical components is shown on one of the bus duct sections, by way of example. Each of the housings 22 is associated with an outlet.

Associated with the duct and housing assembly is a motor 24 and a gas supply or compressor 26 arrangement feeding through tube 28 into the bus duct. The compressor maintains the bus duct at a pressure considerably above atmospheric in order to prevent any gases in the room from entering into the housing 22 containing electrical components where an arc might cause an explosion.

Each outlet is connected by suitable conductors 30 to the buses 16 in a relatively permanent manner. The bus duct and outlet assembly is in this state of electrical connection at the time of the completion of the original installation.

If it is desired to connect motors, for example, to the bus, the housing 22 contains a combination starter for each motor and is mounted to the bus vduct principally by means of the angle member 34 and support member 35 which terminates in the inverted U-shaped portion 37. The portion 37 extends along the top of housing 22 and prevents dust from passing between members 34 and 35 into the back of housing 22. An additional point of connection is by means of metal screws or bolts 36 which are accessible from the inside of the housing 32. The screw 36 cooperates with a switch interlock which insures that the housing 22 be removed only when the main switch is in off position as described below.

Small holes 38 and 40 in the duct and housing 22, respectively, are aligned to permit gas under pressure from compressor 26 to lill the combination starter. The holes in the bus duct are normally plugged when there is no attached combination starter. Mounted behind housing 22 and spaced below duct 14 is a tray 39 for receiving cable 41 leading from the components in the housing to the electrical equipment such as motors to be operated.

Each combination starter will comprise known elements and including a main disconnecting switch or circuit breaker, a magnetically operated `contactor and possibly an overload relay or combination of one or more of such components. These known elements are not Vshown in detail but are indicated generally at 42. Engaging the disconnecting switch or circuit breaker is an interlock indicated diagrammatically at 44 associated with a handle 45 which is operable upon opening of an access door 46 to the housing 32. Upon opening of access door 46,

the interlock system indicated at 44 will open the disconnecting switch or circuit breaker thereby rendering the combination starter inoperative.

The combination starter Vcomponents are electrically connected to the outlet by conductors 48.

The outlet consists of a terminal block 49 having a support of insulating material 50 onto which is mounted a feeder or bus contact 52 which is normally permanently connected to the bus by conductors 30 (FIG. 2). Starter contacts 54 are mounted by bolts 56 to the support Si) spaced from the feeder contacts 52. A suitable connector 58 is associated with each starter contact 54 for the purpose of connecting conductors 48 (FIG. 2) to the terminal block. The terminal block is provided with holes 6i) at either side of the block to permit its being mounted to the bus duct. Also, at either side of the terminal block are hinge supports 62 having holes 64 to receive hinges 66 on a safety disconnect jack 68.

The disconnect jacks consists of a support or cover 70 of insulating material having perpendicularly mounted posts on which are slidably mounted bridging contacts 72. The `bridging contacts are biased toward the terminal block by compression springs 74.

When assembled, the hinges 66 hook into the holes 64 in hinge supports 62 and a spring steel snap 76 holds the cover closed on the terminal block with the bridging contacts 72 in firm engagement with the contacts 52 and 54.

When the disconnect jack of the type shown in FIGS. 4 and 5 is mounted in engagement with the terminal block to bridge the contacts 52 and 54, the connectors 58 are hot or connected through bridges 72 to the bus bars in the ducts. This is an undesirable condition unless there is equipment attached for operation. Consequently, for terminal blocks which are not in use, the cover 70 will be provided with insulated blanks in place of the bridging contacts 72. Thus, the connectors 58 will normally remain insulated from the hot contacts 52.

In summary of the application of the invention, a building preferably would be provided at its original installation with a complete bus duct 14 containing buses 16. Spaced around the bus duct will be outlets 20, each consisting of the terminal block and disconnect jack. Normally, the safety disconnect jack will be provided with blanks of insulating material instead of the bridging contacts 72.

Optional equipment for use in arcas where hazardous combustible gas is present is the motor and compressor unit which maintains the bus duct constantly under pressure greater than atmospheric.

Any time the installation of motors orthe like is desired, the combination starters 22, for example, are mounted on the bus duct, each one enclosing a safety jack. The combination starter is mounted in such a way that it can only bedismounted when the Vaccess door `46 is open, thereby operating the interlock which disconnects the main switch in the combination starter. Thus, while the combination starter is normally under pressure greater than atmospheric provided through holes 38 and 40 in the duct and combination starter housing, when the door is opened to dismount the starter and the high pressure no longer obtains, no undesirable arcing can occur in view of the fact that the interlock has disconnected the equipment from the line. Additionally, the hazard l arising from hazardous atmosphere being ignited by an arcing electrical contact is virtually eliminated.

An alternative form of the invention is shown in FIGS. 6, 7, and 8. In the forms of the invention described heretofore, the line safety jacks and the associated combination starters have been spaced horizontally along a horizontal bus duct. By utilizing the alternative form of the invention shown in FIGS. 6 to 8,the economl of space and convenience in use can be elected. v

Broadly, the alternative form consists in providing a secondary bus duct which receives vertically disposed opname zontally extending bus., A.v plurality of?k combination rstarters are vertically-mounted onthe secondary bu's duct and connected' to associated` line safety jacks.` A vertically? disposedcable ductris mounted adjacent the secondary bus duct and isintegral ltherewithy toreceive cable extending from' the combination. starter to the motors or the like controlled by the combinationstarter The secondary'bus vduct and the adjacent cable duct forms an L`shaped nest towhich each combinationvstarter is mounted. As will be seen from the detailed description below, the distinct components of the system are; insofar as possible, physicallyr isolatedA from each other; communicationA being providedonly for the passage of cable andthe like. The isolation of secondarvduct; cable duct and combination starter all Ifro'nl'one another operates to localize any damage"wh`i`chlmight occur from'a fire. or the like in one of the'.compia'lien'ts;A

Turning to the drawings specifically; the" vertical' unit of the invention is suspended from al section" 100A of the horizontal bus duct liaving` openngsateither endf 102 for the passage of bus'104., The busV ismount'ed' in brackets 106 as describedv inthe embodiments ab've.

Extending downwardlyfrm the horizont'lf'duct se'c` tion 100 is a vertical duct 108" within whichare supported secondary or drop bus 110 connected to the'm'ain bus 104 by soldcrles's connectors 112 boltedor otherwise secured to the main bus 104. j

A vertically extending cable duct 114 is-mounted ad` jacent the secondary duct 108 and forms with itanL shaped structure whichreceives` a plurality ofcontrol unit housings 116 in nesting relationship. In the embodiment illustrated, the secondary duct 108 and the cable duct 114` are formed in'part by a 'generally channel-shaped sheet metal member `118"(.FIG. 7). The secondary duct is closed by a leg" 120 of"mem`ber 118 and a sideplate k122, a plurality of panels 124, and an L-shapedmember 126 which; has a leg 128frming a part of the cable duct114. The ducts -108f and 114 are braced, transversely by spaced angle members 130. The panels 124are removablyl attached'to the angle members130 by screws, bolt'sor other suitable means.'

The cableduct V114 is'formed along! one side b'yfthe plate 122 and the leg'120"of`L`-sh`aped member 12'6.. The back and ,outer side of the secondary duct is formed by a leg 138 of the member 118; The frontof thecable duct is closed by a removable front plate 140;y v f v Vertically spaced line safety jacks 142 of-lthe-type shown in FIGS. 4 andS are fixed in the panels A124 Aformingfa part ofthe front of the secondary busduictllls. Theline safety jacks are connected toa drop bus 110 by leads 144.

Depending upon the rnumber of motors or the like to beoperated fromrthe bus drop 110, a predetermined number of control units such as combination starters are employed, each beingdisposed in itsenclosure orfhousing 116, theenclosures being nested adjacent the'secondf ary bus duct and the cable duct.

No access to the bus drop.is..,necessary through-the starter enclosure because of the line safety jack=and accordingly, substantially complete physical isolation'I of duct and starter isprovided. l The starter housing-116 is formed with a hole which will receive the line safety jack 142 as it extends into the interior of the combination starter housing 116, the line safety jack thereby sealing the hole. A side wall 146 of the combination starter housing 116 adjacent the cable duct 114 has an opening 148 matching a hole 150 in the leg 128, a grommet 152 surrounding the holes to permit the passage of cable indicated at 153. Y y

The grommet 152 of the present invention is illustrated in FIGS. l2 and 13, and comprises an outer ring 154 i forming an annular channel 155 and a web 156 consisting of a plurality of separate sectors 157. Each sector is tapered toward its apex as best illustrated in FIG. 13,

The-'thicker' portion of eachsector urges the sector into the position of FIGulS, therebyzcausing the cable passing' through `to tend to center itself whereas the thinner end portion permits each sector tends to follow the contours of the cable passing 4therethrough in order to maintain, asfcompletelyy as` possible the isolation of the enclosure 116v and the duct114'fr'ox`n each other.

Inspection of FIG. 7 particularlyl will demonstrate the'fisolationfeature ofthe invention. Secondary bus duct`108`7iscompletelyisolated from both the combinationstarter 116 throughl the use of the line safety jack 142 andy the'cablevv` duct 114.

Each combination 'starter is completely isolated from the cableduct 114 except for such minute openings as may be leftbetwe'enthe cable and grommet sectors 157.

FIG.8 shows additional cable duc't sections 158 at the top ofthesecondarly bus duct and adjacent the main bus` duct and 160and at the'bottojrn of the secondary bus f duct; The ductl section 158 has removable end covers 1611and three removable` top plates 1,62, 163 and 164. (FIG. V9). The removable plate 163`permits the attachmentof a'vefticalduct to' the top of the structure for tlefp'a'ssage' of cablef or" control conductors `without disturbing the top cover/tothe horizontal duct section 158Porto`th'e'horizontalbus duct section 100.`

The duct' section 160,h`a'sva removable front cover 166, ai removable' back cover 167 and removable end covers 168. Cablefrom'each'ofth'e combination starters pas-sing throiglr'the cable ,detI 114- will pass 'through` the duct "section's'158 'or,160,` the passage of the cable being permitted b'yftheremvable end covers.` vThe removable back 'cover' 167 'permits the passage-'of cablesfto adjacent units when mounted bak to back'.- ,'Holes170 are formed in'theftp andbttomY of cable `cluet'llfto permit the passage *of the v cablefint thetop' and bottom sections.

The duet' sections, for'exalplf 158, areA terminated at their'lopenleiids'by'vertical-flanges 172 (FIGS. 8, 10 and 11) and* whenjoiii'ed' together4 present two upwardly directed edgesg Vas shown in FIG. 11, acrosswhich cable 153 mustpass'. To .elirr'iiiiateL thewear onk the cables arising "from'the ro'ighf`or"sharp edges'on flanges 172, a U-shaped elongated bridge 174 of plastic rubber or'metalI is mounted on''thei'iiges.` f

It will zbe'not'elwhat" the alternative form of the inventibris designed Atfjperr'nit a plurality of units to be monted side y'fbjfside'j `all being connected to a horizontal bus and 1duet system"asI shown in FIG. 1.. l, A v

In ay generalinanner, while there khas "been disclosed in the `abovedescription,what is deemed to be the most practicaladfeeientembdimentof the invention, it should 'I beiwell understood that the invention is not limited-'to ysuch"ienibtxliment"as"there might be 'changes made inthearangeinnt; disposition and form* of the parts without departing from the principle of the present inventiofasicnljreheded within the scope of theaccompanying claims; g Havingdescribed my invention, I claim: 1.*'An'electrical distribution vsystem comprising a horizontally extending bus duct having'an opening only in the bottomthereof,y aty least one primary bus located in said diret, a'vetieall'y"extendii'igy bus 'duct having closed vertical` vvalls'fandf'an opening |at the top thereof, said verticalfdtctbe'ng'ijoinedto said horizontal duct withfsaid openings-"alig1'ied;3 at least""one*secondary bus dropping from said primary bus and disposed in said vertical duct,

Vwalls of said cable duct and housings having small aligned openings for the passage of cable between each said housing and cable duct, means for sealing said openings around said cable, and horizontal cable ducts `at the top and bottom of said cable duct and having openings communicating with said cable duct, said horizontal ducts including walls forming barriers `to isolate said horizontal ducts from said bus ducts and from said control unit housings.

2. An electrical distribution system comprising a horizontally extending bus duct having an opening `only in the bottom thereof, at least one primary bus located in said duct, a vertically extending bus duct having closed vertical walls and an opening at the top thereof, said vertical duct being joined to said horizont-al duct with said openings aligned, at least one veritcal bus dropping from said primary bus and disposed in said secondary duct, a plurality of closed control unit housings secured in vertical alignment to a wall of said vertical duct, control units in said housings, an electrical connector unit mounted in the adjoining walls of each said housing and said vertical duct to provide electricalY communication between said secondary bus and said control units, a vertical cable duct having closed vertical walls, one of the -walls of said cable duct adjoining a wall of each said housing, the adjoining walls of said cable duct and housings having small aligned openings for the passage of cable between each said housing and cable duct, and means for sealing said openings around said cable.

3. An electrical distribution system comprising a horizontally extending bus duct having an opening only in the bottom thereof, at least one primary bus located in said duct, a vertically extending bus duct having closed vertical walls and an opening at the top thereof, said vertical duct being joined to said horizontal duct with said openings aligned, at least one secondary bus dropping from said primary bus and disposed .in said Vertical duct, a plurality of closed control unit housings secured in vertical lalignment to a wall of said vertical duct, control units in said housings, an electrical connector unit mounted 1n the adjoining walls of each said housing and said vern tical duct to provide electrical communication between said secondary bus and said control units, a vertical cable duct having closed vertical walls and openings at the top and bottom thereof, one of the walls of said cable duct adjoining a wall of each said housing, the adjoining Walls of said cable duct and housings having small aligned openings for the passage of cable between each said housing and Icable duct, and a flexible resilient grommet disposed in said aligned openings, said grommet having an -annular channel embracing the walls of said housing and cable duct and a web in the central area thereof, said web being `formed of a plurality of separate sectors tapering toward their apices, said sectors engageable with said cable to reduce the size of the openings in said` walls.

4. An electrical distribution system comprising a horizontally extending bus duct having an opening only in the bottom thereof, at least one primary bus located in said duct, a vertically extending bus duct having closed vertical walls and an opening at thertop thereof, said vertical duct being joined to said horizontal duct with said openings aligned, at least one secondary 4bus dropping from said primary bus and disposed in said vertical duct, at least one closed control unit housing secured to a wall of said vertical duct, a control unit in said housing, an electrical connector unit mounted in the adjoining wall of said housing and said vertical duct to provide electrical communication between said secondary bus and said control units, a vertical cable duct having closed vertical walls and an opening in at least one end thereof, one of the walls of said cable duct adjoining a wall of each said housing, the adjoining walls of said cable duct and housing having small aligned openings for the passage of cable between said housing and cable duct, means for sealing said openings around said cable, and at least one horizontal cable duct at the open end of said cable duct and having an opening communicating with said cable duct, said horizontal duct including walls forming barriers to isolate said horizontal duct fromsaid bus ducts and from said control unit housing. 5. An electrical distribution system comprising a hori` zontally extending bus duct having an opening only in the bottom thereof, at least one primary bus located in said duct, a vertically extending bus duct having closed vertical walls and an opening at the top thereof, said vertical duct being joined to said horizontal duct with said openings aligned, at least one secondary bus drop-` ping from said primary bus and disposed in said vertical duct, a plurality of closed control unit housingsI secured in vertical alignment to a wall of said vertical duct, control units in said housings, an electrical cor1- nector unit mounted in the adjoining walls of each said housing and said vertical duct to provide electrical communication between said secondary bus and said control units, a vertical cable duct having closed vertical walls, one of the walls of said cable duct adjoining a wall of each said housing, the adjoining walls of said cable duct and housing having openings for making electrical communication between each saidV housing and cable duct and means for sealing said openings.

References Cited in the iile of this patent UNTTED STATES PATENTS 913,024 Meacham Feb. 23, 1909 1,037,010 Irons Aug. 27, 1912 1,342,545 Krantz lune 8, 1920 1,434,897 Howell Nov. 7, 1922 1,697,814 Forbes Ian. 1, 1929 1,857,711 Dante May 10, 1932 1,894,675 Dixon Jan. 17, 1933 1,955,287 Graves Apr. 17,` 1934 1,956,439 Frank Apr. 24, 1934 2,041,675 Frank May 19, 1936 2,147,023 Frank Feb. 14, 1939 2,219,250 Bramhall Oct. 22, 1940 2,319,415 Lightfoot May 18,` 1943 2,427,742 lPeterson Sept. 23, 1947 2,542,853 Wills Feb. 20, 1951 2,619,515 Doane Nov. 25, 1952 2,648,032 Meltelburg Aug. 4, 1953 2,708,927 Dixon May 27, 1955 2,766,614 Cook Oct. 16, 1956 2,829,317 Timmermans Apr. 1, 1958 2,832,406 Turenne Apr. 29, 1958 2,859,390 Baker Nov. 4, 1958 2,891,101 Koliss June 16, 1959 UNITED STATES PATENT OFFICE s CERTIFICATE 0F CORRECTION Patent No', 3,003,084 i i l l october 3, 1961 Weldon Cfwilkinon` y l I i l It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read s.sI "corrected below.

Signed and sealed this 27th day of [March `1962.

SEAL) Attest:

ERNEST W. lSWIDERl y DAVID L. LADD Attesting Officer i v Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE 0F C0RRECTI0N Patent N, 3,003,084 l l Y october 3v 1961 l Weldon C. lWilkinson, i l I l It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read as "corrected below.

Column 7, line l5, for "veriftcal" read V secondary line 16, forl "secondary" read vertical Signed vand sealed this 27th day of [March `1962.

SEAL) Attest:

ERNEST w. SWIDIIRl DAVID L. LADD Attesting Officer l Commissioner of Patents 

